1 /*
   2  * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "utilities/globalDefinitions.hpp"
  26 
  27 class Unsafe {
  28 public:
  29   // Note: The VM's obj_field and related accessors use byte-scaled
  30   // ("unscaled") offsets, just as the unsafe methods do.
  31 
  32   // However, the method Unsafe.fieldOffset explicitly declines to
  33   // guarantee this.  The field offset values manipulated by the Java user
  34   // through the Unsafe API are opaque cookies that just happen to be byte
  35   // offsets.  We represent this state of affairs by passing the cookies
  36   // through conversion functions when going between the VM and the Unsafe API.
  37   // The conversion functions just happen to be no-ops at present.
  38   enum {
  39     final_bits   = 1,
  40     offset_bits  = BitsPerLong - final_bits,
  41 
  42     final_shift  = 0,
  43     offset_shift = final_bits,
  44 
  45     final_mask   = right_n_bits(final_bits)
  46   };
  47 
  48   static jlong field_offset_to_byte_offset(jlong field_offset) {
  49     return (field_offset >> offset_shift);
  50   }
  51 
  52   static jlong field_offset_from_byte_offset(jlong byte_offset, bool is_final = false) {
  53     return (byte_offset << offset_shift) | (is_final ? final_mask : 0);
  54   }
  55 
  56   static jint invocation_key_from_method_slot(jint slot) {
  57     return slot;
  58   }
  59 
  60   static jint invocation_key_to_method_slot(jint key) {
  61     return key;
  62   }
  63 };
  64